1. Field of the Invention
The present invention relates to the field of semiconductor wafer processing and, more particularly, to an apparatus and method for customizing electrode contact placement on a semiconductor wafer while depositing and/or removing a material on a semiconductor wafer.
2. Description of the Related Art
In the manufacture of devices on a semiconductor wafer, it is the current practice to fabricate multiple levels of conductive layers on a substrate. In order to fabricate features, circuits, and devices on a substrate, such as a semiconductor wafer, various techniques may be used to deposit and etch materials on the substrate. Deposition techniques include processes such as physical vapor deposition (PVD), chemical vapor deposition (CVD), sputtering, and immersion of the substrate in an electrolyte solution. This last technique may be used for either electroless deposition or electroplating.
Similarly, a number of techniques are known for removing a material from a wafer. These techniques include reactive ion etching (RIE), plasma etching, chemical-mechanical polishing (CMP), and immersion of the wafer in an electrolyte solution. Material removal by subjecting an immersed wafer to an electric field employs an equivalent set-up to that used for electroplating, but with an opposite result since in this instance charged particles are removed rather than deposited on the wafer.
During the electroplating/electropolishing process, the wafer is immersed in an electrolyte solution and positioned in an electric field between a cathode and an anode such that charged particles are deposited/removed onto the surface of the wafer. More specifically in the electroplating technique, an anode is placed within the electrolyte solution and a cathode is brought into contact with the wafer.
In the past, the chuck or platform on which the wafer rested during processing acted as the cathode to create a uniform potential base across the bottom surface of the wafer. However, with the potential created along the bottom surface of the substrate, a potential gradient often resulted with the face of the wafer (the upper surface of the wafer being processed) due to resistance in the thickness of the wafer. Further, because a uniform potential was created across the bottom surface of the wafer, a potential gradient across the surface of the wafer could not be measured to determine resistance characteristics of the wafer.
The above problems may be avoided, however, by bringing the cathode into contact with the outer edge of the face of the wafer. Although a single cathode contact along the periphery of the face of the wafer being processed is sufficient to create the desired electric field, a more uniform current distribution across the wafer may be achieved by using multiple points of cathode contact around the outer edge of the wafer face. The points of cathode contact along the outer edge of the wafer face, however, must circumvent the design layout of the fabricated features, circuits, devices, etc. that are formed on the surface of the wafer.
For example, FIG. 1 shows the face of a processed wafer and identifies the unprocessed space along the periphery of the processed wafer as the scrap area 2. The specific size and shape of the scrap area of a given wafer is dictated by the specific design layout on the surface of that wafer. Thus, the placement of the cathode contacts must be pre-determined with respect to the final design layout of a processed wafer. FIG. 2 illustrates an example of the placement 4 of eight cathodes used to create a potential across the wafer. This particular cathode contact scheme, however, might not work with another wafer, depending on the intended design layout of the processed area. In such a case, either the processed area would have to be redesigned such that it did not coincide with the cathode contacts, or the processing equipment itself would have to be altered or replaced with equipment having the cathode contacts in the correct position for the given wafer. Each of these options is costly, time consuming, and inconvenient.
Current processing equipment typically consists of a processing chamber with the cathode(s) in a fixed position. The cathode(s) contact each wafer placed in the processing chamber at the same location on each wafer processed. If the point of cathode contact needs to be moved due to a change in the design layout of the wafer being processed, the processing chamber has to be replaced with one having the cathode(s) fixed in a different position. Thus, an apparatus that could couple to the processing equipment and allow a wafer manufacturer to easily change the number of cathode contact points and the cathode contact positions on the wafer during processing is desirable.